Electroinductive sensing device with adjustable coil



A. I. ARNELO June 30, 1970 ELECTROINDUCTIVE SENSING DEVICE WITH ADJUSTABLE COIL 4 Sheets-Sheet 1 Filed Jan. 20, 1967 FIG./

June 30, 1970 A. l. ARNELO 3,518,533

ELECTROINDUCTIVE SENSING DEVICE WITH ADJUSTABLE COIL Filed Jan. 20, 1967 4 Sheets-Sheet 23 ELECTROINDUCTIVE SENSING DEVICE WITH ADJUSTABLE com Filed Jan. 20, 1957 A. I. ARNELO June 30, 1970 4 Sheets-Sheet 5 A. l. ARNELO .Yune 30, 1970 4 Sheets-Sheet 4 Filed Jan. 20, 1967 3,518,533 ELECTROINDUCTIVE SENSING DEVICE WITH ADJUSTABLE COIL Anders Ingvar Arnelo, Vasteras, Sweden, assignor to Essem Metotest AB, Skultuna, Sweden Filed Jan. 20, 1967, Ser. No. 610,511 Claims priority, applicatigzn/ggveden, Feb. 14, 1966,

9 Int. Cl. G01r 33/12 US. Cl. 324-40 ABSTRACT OF THE DISCLOSURE A system of probe coils for the non-destructive electroinductive testing of materials wherein be tested is moved in the axial direction of the coils or the coils are moved in the axial direction of the material, in such a way characteristics of the coils vary as a properties of the material, the variations of said electrical characteristics being measured for the purpose of determination of said properties; some of the coils are centered about individual non-coincident axes; the coils are surrounded by the material or the material is surrounded by the coils.

invention relates to an electroinductive eddy currents induced in material under direction of the induction The present sensing device for relative movement, in the axial coil system, between the material It is known in the non-destructive testing of materials to utilize so called electroinductive testing. In this context the material to be tested is passed between a coil which is connected to a source of alternating current. An electromagnetic field is formed in when the force lines of the field cut the test piece in the same which react on the coil and its electrical properties so that these vary as a function of the eddy currents in the sample material, which in turn vary, depending on the different properties of the said sample material. By measuring the electrical data of the coil it is thus possible to check the properties of the sample material. Since, however, the variations in the property of the coil are very small in themselves the coil must be included in a bridge or compensation circuit of some arbitrary type and the unbalanced voltage obtained from the bridge must be greatly amplified so that said variations can be indicated. Such bridge circuits are previously known per se and do not constitute a part of the invention proper, and consewill not be described in detail. A suitable embodiment of such bridge circuits is described, for instance, in

Pat. 179,407 and on pages 92 and 93 in Progress in Non-destructive Testing," published by E. G. Stanford and I. H. Fearon, vol. 1, Heywood & Company Limited, London, 1958. Electromagnetic testing of material is taken up in more detail in the section Electromagnetic methods of testing metals (pages 59-109) in the same book.

bridge circuits are provided with one or, at the most, two active branches, i.e. branches which include a coil possessing the aforementioned properties. In the case of the present invention, however, it is preferred to allow more than two branches to include such an active coil, since in this way it is possible to adapt the coil systern to the sample material undergoing the test.

The magnitude and extension of the eddy currents are influence by a large number of different factors, i.e. e coupling between coil and test sample, which depends on the distance from the turns of the coil to the sample material. Other factors are the shape of the sample, its conductivity and its magnetic properties. When testing material for faults by means of the electroinductive method and the sensing device. 3

United States Patent 1 Claim 10 the material to 3,518,533 Patented June 30, 1970 important to eliminate the effects of all factors other than those which are connected with the faults in the material. For this purpose it is necessary, among other things, to ad ust the coupling factors to the samples in question or, in other words, to adjust the dimensions of the coil to the dimensions of the sample material. This means that according to the known technque one is forced to use coils of different dimensions for testing material of different dimensions. When testing, for instance, rod material of different cross-section and different dimensions it is thus necessary to use a large number of coils of different types. This is obviously an eco norriic problem which con d be avoided if one and the same sensor could be used for testing material of different dimensions. The invention is intended to make this possible.

An electroinductive probe according to the invention is mainly characterized in that the induction coil system comprises at least two coils positioned one after the other in the axial direction and capable of being adjusted relative to each other transversely to said direction.

Additional characteristics of the invention are from the claim.

The invention will be described more closely with reference to an embodiment of an electroinductive sensor shown in the accompanying drawing.

FIG. 1 shows diagrammatically an embodiment of an electroinductive probe means according to the invention, provided with adjusting means for the induction coils init is therefore evident 0 cluded in the same.

FIG. 2 shows a wiring diagram for an electric circuit, in which the probe means according to the invention is connected.

. FIGS. 3 and 4 illustrate the relative movement carried out between probe and sample material, as well as show ing additional examples of probe co'ls surrounding the sample material whilst such mechanical means as t e previously mentioned adjusting means for the coils are omitted. FIG. 5 shows the sample material surrounded by probe coils.

FIGS. 6 to 10 show various forms of sample material with probe coils adapted thereto.

FIGS. 11 and 12 illustrate examples where the planes of movement of the probe coils form angles other than with axial direction of the sample material (advancing direction).

The induction coil system in FIG. 1 is provided with four coils 1, 2, 3 and 4 each arranged to be displaced in respective holders in different directions on actuation of an operating wheel 22. The wheel 22 is secured to a shaft 21 which is provided with four identical earns 16 arranged with a mutual displacement of 90 on the shaft 21. Each cam 16 abuts one end of a rod 20, the other end of which is pivotally connected to a second rod 17. Each coil 1, 2, 3, 4 is securely connected to a rod 17.

As shown in f FIG. 1, the coil 1 moves downwards in the direction of arrow 14, the coi 3 upwards in the direction of arrow 15, the coil 2 to th left in the direction of arrow the righ in the direction of arrow 19.

The passage located in the induction coil system fc passage of the test piece therethrough will obviousi decrease from the maximum opening shown in the draw ing when the wheel 22 is actuated to move the coils in tl direction of arrows 14, 15, 18, 19. The induction or system can thus be adjusted to test pieces of differe cross-sectional area.

In the wiring diagram of FIG. 2, there is shown a t iece 5 with the coils 1, 2, 3, 4 arranged in sequer therearound. Alternating current is supplied from a v( age source 10 via a transformer 9 to two corners of bridge and an unbalanced signal is taken out from the The arrangements illustrated in FIGS 6 to 12 ma two remaining corners on the output terminals 11 when, have ad usting means as the arrangement of FIG 1 In for instance, the electric properties are different in the t e arrangements of FIGS. 3 to which have only two portions of the test piece 5 sensed by the separate coils coils, the mutually eccentric positions of the coils are 1, 2, 3, 4 at a particular time. This signal can be used to adapted to the dimensions of a certain test piece In such actuate an indicating means which colors the faulty part a case, according to the invention the coils may be fixed of the material. in position in relation to each other, which means that IG 3 shows an example where the coils I, 2 are stathe coil arrangement can be manufactured to assume such tionary while rod material 5 to be tested are fed for exfixed positions. ample, from a rolling mill and thereby is displaced, at The invention is not restricted to the described emright angles to the plane of the coils 1, 2 in the direction bodiments which are intended for non-magnetic test of arrow 6 FIG 4 illustrates an example where the test pieces, but can also be adapted with magnetic test pieces, piece shown as a rod is driven by appropriate mechanical providing that the test piece 1S magnetically saturated driving means through the coils in a helical movement at is claimed is: represented by the arrows 6, i.e. a helical sensing of the 1. An electroinductive sensing device for use in deest piece is effected Conversely, the coils 1, 2 may be termining the properties of a piece of material to be tested displaced and/or rotated by appropriate mechanical dri'vuring its movement relative to an induction coil system ing means while the test piece 5 remains stationaiy FIGS. comprising at least two coils, individually encircling said 3 and 4 show the test piece 5 surrounded by the coils test piece and having their axes parallel to the longitudi FIG. 5 shows two coils 1, 2 surrounded by the test nal axis of said test piece and being positioned the one piece 5, which in this case is a tube with its center alon after the other in the longitudinal direction of said test the line 8 The coils 1 2 can be displaced or effect a ropiece, whereby during such movement the electrical char tational movement relative to the test piece 5 or the test acteristics of said coils vary in response to the properties piece 5 can be moved ielative to the coils 1 of said test piece said device further comprising a meas- FIGS 6-10 illustrate embodiments of the coils 1 2 3, uring means connected to said 0011 system for measuring shown as single turns of wire and their positioning at the variations in said electrical characteristics, and ad ustditferent sections of the test piece 5. The coils 1, 2,3, 4 ing means coopeiating with at least one of said coils to are positioned in plane 12 at right angles to the longitudioffset the same, prior to the use of said sensing device, nal axis 8 of the test piece FIG. 6 shows the test piece from the other coils in a direction transverse to said in the form of a rod, FIG. 7 shows the test piece in tubulongitudinal direction and maintaining said coil in said lar form FIG 8 shows the test piece of square crossadjusted position during the measuring. section FIG 9 shows the test piece of U-shaped crosssection, FIG. 10 shows the application of the sensing References Cited device of the invention to a test piece of triangular c'ross- UNITED STATES PATENTS section which, for instance, resents one angle of 120 3 The electioinductive sensing device may thereby be pro- 1129584 2/1915 Murphy 324 37 vided with an odd number of adjustable coils, an addi- 2267884 12/1941 ZPSChIag 324* tional but stationary coil being arranged in a plane per- 2337352 12/1943 slhterson et a] 324*41 2,882,488 4/1959 Price et al. 324-37 pendicular to the axial direction. FIG. 9 shows an exam ple having two coils 1, 4 for externally sensing the test 40 2124579 7/1938 Knerr et a] X 2,435,985 2/1948 Stewart et al. 324*34 piece and two coils 2, 3 for sensing the test piece in 3 29 ternally. The inner and outer coils can also be used in the 9350 1 1967 Tompkins et case of tubular test pieces, as shown in FIG. 7 FOREIGN PATENTS FIG. 11 shows two coils 1, 2 lying in planes which form certain angles to the planes 12 at right angles to, the 827527 2/1960 Great Bntam' longitudinal axis 8 of the test piece The planes of these :oils 1 and 2 are mutually parallel. FIG. 12 shows how ALFRED SMITH Pnmaly Exammer raid planes for the coils 1, 2 are also capable of forming US Cl. X'R t certain angle to each other. 3 24-37 

